Armand de Gontaut, Baron of Biron in the context of Jeanne d'Albret

Charles de Gontaut, 1st Duke of Biron (1562 – 31 July 1602) was a French noble, military commander, Admiral of France, Marshal of France, and governor of Burgundy during the final days of the French Wars of Religion. The son of Marshal Armand de Gontaut, Baron of Biron who had served the crown militarily throughout the religious wars, Biron made his entry into French politics in the late 1580s. Initially a follower of the chief royal favourite Épernon by 1589 he was a candidate to become Admiral of France. In August 1589 Henry III of France was assassinated, and Biron and his father transferred their loyalties to the Protestant Henry IV of France, putting them at war with the Catholic League. He fought at the royalist victories of Arques and Ivry in late 1589 and early 1590, during which he developed a reputation as an exceptional commander. In 1592 he became Admiral of France, a post he held for two years, before being compelled to trade it for the title of Marshal so that the former title could be offered to a rebel. In 1593 Biron invaded Burgundy, and succeeded in capturing many villages, but was unable to secure any major cities. In 1595 he again invaded Burgundy with considerably more success, Beaune, Auxonne, Autun and finally Dijon falling to him in late May of that year. During the campaign, Henry granted him the governate of Burgundy. A Spanish army under the Constable of Castilla invaded in response and joined forces with the duke of Mayenne, lieutenant-general of the League. Having called on Henry for support, Biron and his king defeated the Constable and duke against the odds at the Battle of Fontaine-Française.

This largely marked the end of the domestic civil war, as the conflict transformed into an international one against Spain. In 1597 Biron led the successful siege of Amiens, the city having recently been taken by surprise by the Spanish. He signed the Treaty of Vervins with the Spanish the following year. He was then tasked with making war on the duke of Savoy which he conducted for the next few years, seeing continued success. Around this time, he began to be courted by the Savoyard duke, who saw in his tense relations with Henry the potential for a useful defection. According to the testimony of Jacques de La Fin, Biron entered a formal treaty to betray Henry in 1600, by whose terms he would be established as a largely independent ruler of Burgundy under the overall authority of the Spanish, in return for his betrayal of Henry. No such treaty has however ever been found.